ObservableListViewCore run filter method for all items when adding a new item

[Gusi]

Using ObservableListViewCore to filter an ObservableCollection, I've observed that the Filter method is executed for all items in the collection when adding a new item to the initial ObservableCollection.

In contrast, using CollectionViewSource only executes the filter for the added element, and this is a huge performance benefit with large collections. CollectionViewSource only runs Filter method for all items when calling Refresh on the view.

I'm not sure if this is an indented behaviour, so I don't know if call it a bug, or to propose it as an enhancement over the current implementation.

Thanks!

[jbe2277]

This is by design.

From a performance point of view the Filter and the Sort are not the critical path. The critical path is InnerList.Merge because this raises the CollectionChanged event which is often used to trigger UI updates. The Merge implementation is optimized in that regard.

waf/src/System.Waf/System.Waf/System.Waf.Core/Foundation/ObservableListViewCore.cs

Lines 117 to 124 in 2b14be8

	private void UpdateInnerList()
	{
	var enumerable = originalList;
	if (Filter != null) enumerable = enumerable.Where(x => Filter(x));
	if (Sort != null) enumerable = Sort(enumerable);
	var newList = enumerable.ToArray();
	InnerList.Merge(newList, comparer, Insert, RemoveAt, () => Reset(newList), Move);
	}